# Equilibrium

The market is in equilibrium when supply equals demand. $$Q_S = Q_D$$

## Example

The market for cookies is huge, with many consumers and many sellers.

The supply follows the equation Q_S = 3 P.

The demand follows the equation Q_D = 10 - 2 P.

In equilibrium, supply equals demand \begin{align*} Q_S &= Q_D \\ 3 P &= 10 - 2 P \\ 5 P &= 10 \\ P &= 2 \end{align*}

In equilibrium, a banana is sold for \$2 and there are 6 bananas on the market.

### Question

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